Piezoelectric crystals or quartz resonators, are well known and widely used in the art, and are particularly applicable in the use of high frequency filter networks, such as in radios or other communication devices. One important concern in radio design is the adjustment of the matching components to the crystal filter in the crystal filter network to take into account the loading effects of external components. Thus, appropriate matching is necessary in order to achieve the desired output response waveform in terms of sufficient bandwidth, center frequency, and minimization of ripples. Typically, this adjustment is accomplished in a radio factory by laser trimming matching components such as an inductor or a capacitor that form a tank circuit for matching the input and/or the output of the crystal filter. This extra factor trimming step adds to the cost and cycle time of the radio.
In conventional approaches, the cost of the radio is driven higher than necessary because an expensive crystal filter having an extra wide bandwidth was necessary to compensate for the changing crystal filter network characteristics over temperature. For example, as temperature changes, the center frequency of the filter response waveform of the crystal filter network changes. This is due to changes in the crystal filter itself, the matching networks, and surrounding radio subsystems. However, since the traditional crystal filter has a much wider bandwidth than is needed for room temperature operation, the desired frequency can still pass through the crystal filter network even when the center frequency of the filter has shifted over temperature. A need, therefore, exists for eliminating the radio factory laser trimming of the crystal filter match and to substitute a less costly crystal filter having a narrow bandwidth, while still maintaining an optimum crystal filter network performance over temperature.